<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    var a = 3;        //引号的数字，表示字符


    var b = "4";

    var c = a + b;      //左右，有一方为字符串型时，作为连接功能

    alert(c);
</script>
</body>
</html>